The Hellgate: London demo has just been released by Flagship.
You can download a 1.45gb copy for free on the link above. The demo only lasts for 4 levels but you get to know your way around the game and the quests, and whether or not you'll buy it.
Hellgate has had mixed reactions so far. It's been compared to the Diablo franchise as its made by the creators of that game, but it's much more action-orientated.
There are 2 ways of playing the game, offline and online. If you want to play offline, you just buy the game and play solo content, if you want to play online, you have to subscribe. It's a bit like Phantasy Star Online was, but since I'm already tossing up between City of Heroes and World of Warcraft, I'm not sure I want a 3rd online game to occupy my time.